The breech chamber according to the present invention is primarily intended to be used in connection with ammunition units having separately housed charges. In such ammunition, the propellant charge is separated from the projectile, shell or the like during the ramming procedure. The ramming of the projectile, shell or the like as well as the propellant charge can be carried out automatically or by hand. Various types of bag charges with or without cartridge cases can be used.
When the projectile, shell or the like is rammed into the beginning of the rifled portion of the bore of the barrel, the driving band of the respective ammunition unit prevents the combustion gases from the propellant charge from spreading into the bore of the barrel. The driving band is made of a comparatively soft material, such as copper, plastic, iron or the like. During ramming it is important that approximately the same ramming force can be achieved under different ramming conditions, in order to limit the variation of the muzzle velocity for different projectiles and for different firing elevations. Also, when firing in the most elevated position, the ramming force must be sufficient to ensure that the rammed ammunition unit does not fall backwards. Different muzzle velocities always mean a reduced hit probability.
In order to attain a more exact ramming, efforts have previously been concentrated on the ammunition and not so much on the design of the breech chamber.